I'm not sure that I buy that they were all looking for a way out. But, for the sake of argument, let's say they were. All that means then is that there's no need to rescue them until there's an overriding reason, say the 50th Anniversary!

We already know that they're visited at least one more time and more likely two (one for River to tell Amy to write the last page, and one in which to retrieve the book to slip it into the Doctor's coat).

Also, if they were all looking for a way out, I'm sure there'd be something better than dumping them in the past, separated from friends and family.

It obviously wasn't a plan, but the situation worked out. And, again, why risk destroying the world just to screw up their happy little lives when they are, you know, happy where they are. Especially since we know they can still be visited from time to time.